This invention relates to the field of borehole measurement while drilling (MWD). More particularly, this invention relates to the communication of control information from the drilling rig floor to the MWD instrumentation system when it is situated downhole near the bottom of the drill string.
An MWD system may consist of a number of sensors connected to a computer based data acquisition system. The computer collects the information from the sensors and digitizes and formats this information for downhole storage and for binary data transmission to the surface. Relevant parameters of the data collection and formatting process are stored according to preprogrammed instructions residing in the computer's memory.
Current state of the art of MWD data transmission is via mud pulse telemetry. Data communication rates achievable with this technology is on the order of one bit per second. As the number of sensors developed for downhole application increases, the time required to transmit all the data increases. Further, information update requirements of certain parameters may vary depending on conditions arising during the course of drilling. Unfortunately, there is not now an efficient and reliable method of relaying control information from the drill rig at the surface downhole to the MWD system so as to effect a change in operation of the system (e.g. an operational mode change). Presently, the MWD system must be raised to the surface where operational changes are input to the computer. Thus, it would be advantageous to be able to alter the operating modes of the MWD system without removing it from the borehole. Affecting a change without removal would save a substantial amount of time in the drilling process and therefore afford considerable cost savings.